When information bits are encoded by a channel coder, the channel coder outputs a codeword including the information bits and redundancy bits added to the information bits. An example of the channel coder is a systematic channel coder such as a convolutional turbo code (CTC).
Among modulation methods, quadrature amplitude modulation (QAM) is a modulation method that converts multiple bits of transmission data into information of phase and amplitude of one symbol, and transmits the bits. A 16-QAM method can transmit 4 bits with one symbol and a 64-QAM method can transmit 6 bits with one symbol.
For example, the 16 QAM divides data to be transmitted into 4-bit units, mapping each of the units to one of 16 symbols, modulating them, and transmitting them, and it generally uses the gray mapping for the symbol mapping method. When the 4-bit symbol that is modulated by the gray mapping is received, the bits of the received symbol respectively have different reliability. For example, the reliability of the received bits can be shown as log likelihood ratio (LLR) values. Performance of the received symbol, for example a block error rate (BLER), may vary depending on how the codeword is mapped in the symbol due to the difference in reliability.
Further, in the wireless communication system, when a transmitted packet is not normally received in a receiver, a method for retransmitting the corresponding packet is used. The retransmission method includes, for example, a hybrid automatic repeat request (HARQ). In the retransmission method, reliability should be considered in order to improve performance of the received packet.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.